Photographic paper



y 1940- .1.- s. CUMMINGS 2,207,695

PHOTOGRAPHIC PAPER Filed 001:. 28, 1938 BLUSHED FILM PHOTOGRAPHIC EMULSION I5 DISCRETE PARTICLES BASE PAPER CLEAR ENVELOPE I3 II I I4 INVENTOR JOHN s, CUMMINGS A TTORNEY Patented July 9, 1940 UNITED STATES PATENT OFFICE PHOTOGRAPHIC PAPER Application October 28, 1938, Serial No. 237,449

3 Claims.

This invention relates to photographic paper, and has particular reference to a photographic paper comprising a cellulose base, a film of blushed cellulose derivative composition over 5 the paper, and a film of photographic emulsion thereon, whereby improved color, moisture resistance and resistance to change in dimensions is obtained.

The phenomenon of blushing is one well known to the coating industry. While unpigmented coating compositions which dry by evaporation of solvent (lacquers) generally dry down to smooth homogeneous transparent films, it is possible to produce non-homogeneous films by disturbing the solvent balance so that the binder is insoluble in the solvent during some portion of the film-forming operation, and remains insoluble thereafter. In such cases, the binder precipitates out in the form of very small discrete particles of transparent material, with air between the particles; the resultant film is translucent or opaque, appears white to the eye and is generally matte. Nitrocellulose, other cellulose derivatives and resins all can be made to yield such films, either by proper choice of organic solvents, or by judicious use of water in the film; the methods of producing such films are well known in the art, largely because a knowledge of the conditions which favor blushing permit formulators to avoid this generally undesirable phenomenon. This type of matte translucent opaque white film has heretofore been used to coat cloth and paper, to produce tracing cloth.

In my co-pending application, Serial Number 75,570, filed April 21, 1936, I have disclosed the possibility of controlling the solvent balance in such compositions so that the film deposited during the early stages of drying is clear and transparent, while the film deposited in the late stages is blushed and opaque, whereby a blushed film is obtained enclosed in a glossy envelope, yielding a glossy opaque finish for paper and the like.

I have discovered that such blushed film, when Ordinary coated papers are made by treating ordinary paper with dispersions of pigment in binding materials; because the paper mustbe (c1. 9s-s) both cheap and white, water-soluble binders are chosen, since the cheap white pigments are opaque in such binders while transparent or translucent in water-insoluble binders. When suchpapers are coated with photographic emul- 6 sions, the water in the emulsions quite naturally disturbs the paper somewhat; and the water used in the developing and fixing baths has a similar effect. The principal difficulty with conventional papers is due to this tendency to absorb 10 water-when the prints are dry, they often vary in dimensions slightly when compared with the original, due to the fact that the moisture content cannot be controlled accurately.

When paper is coated with a blushed film of a cellulose derivative composition, a white coated paper is obtained without any pigment, together with a film of water-insoluble binder. If the film is encased in a glossy envelope of clear lacquer, a glossy coated paper is obtained with a water resistant film, which seals in any water-insoluble impurities which may be in the paper stock. When a gelatin silver salt emulsion is applied to such a paper, no softening of the paper occurs, so that a uniform thin film of silver emulsion may be applied, thus spreading out the emulsion evenly and permitting the use of less of it to get the desired results. The principal advantage, however, is that the film does not absorb water during developing and fixing, thus ensuring faith- 30 iul reproduction of the original negative.

Such a photographic paper is shown in the accompanying drawing, which is a section through a sheet made according to my invention. As shown therein, the finished article comprises a base ll, coated with a film I 2, comprisingdiscrete particles l3 embedded in a clear envelope l4, and having a top coat comprising a photographic emulsion I5.

Typical examples of my invention are: 4(

Example I Parts by weight SS nitrocellulose 5 sec. (wet with 30% butyl alcohol) 13.8 Acetone 5.0 45 Methyl alcohol (C. P.) 74.4 Water 4.2 Glycerine..- 2.6

This lacquer was coated on regular uncoated photographic paper stock, and allowed to dry, to give a glossy coated paper with an opaque, very white blushed film enclosed in an envelope of clear lacquer.

This paper was then coated with a photographic emulsion having the following formula:

A solution is made of Grams Gelatin 1 Potassium bromide 88 Citric acid 50 Distilled water 1600 This solution is heated to 35 C., and a cold ammoniacal silver nitrate solution is added to it,

of the following formula:

Grams Water 400 Silver nitrate 20% ammonia water The mixture is maintained at 35 C. for 30 minutes, and allowed to gel overnight, then cut into threads, and washed carefully. This emulsion was heated to 40 C., and 150 grams of gelatin was added; the heating was continued until the gelatin was thoroughly absorbed, and the emulsion ready for coating on the paper.

The resultant paper was free from the water absorptive tendencies of ordinary paper, and gave prints absolutely free of distortion.

Example II Parts by weight A; sec. SS nitrocellulose (wet with 30% butyl alcohol) 5 sec. SS nitrocellulose with 30% butyl alcohol) 5.0 Butyl stearate 1.5

Cocoanut oil, treated (Wecoline Plasticizer) 2.7 Ethyl acetate (B. P. 77 C.) 24.0 Toluol (B. P. 117 C.) 28.9 Xylol (B. P. 142 C.) 20.9

Total 100.0

Paper coated with this lacquer gave results similar to that obtained with the lacquer of Example I.

Example II! Parts by weight /4 sec. SS nitrocellulose (wet with 30% butyl alcohol) 19.0

5 sec. SS nitrocellulose (wet with 30% butyl alcohol) 5.7 Butyl stearate 2.4 Wecoline 4.3 Acetone 20.6 Toluol 38.0

Xylol 10.0

Total 100.0

This lacquer gave a somewhat more flexible film than the lacquers of Examples I and II,

examples without departing from my invention,

which is defined in the claims.

I claim:

1. A photographic paper comprising a cellulose base, a continuous, glossy blushed film of cellulose derivative on said base, and a photographic I emulsion on said blushed film.

2. A photographic paper comprising a cellulose base, a blushed film containing cellulose derivative on said base comprising discrete particles containing cellulose derivative enclosed in a glossy envelope of cellulose derivative lacquer and a photographic emulsion on said blushed film.

3. A photographic paper comprising a cellulose base, a blushed film containing nitrocellulose on said base comprising discrete particles containing nitrocellulose enclosed in a glossy envelope of nitrocellulose lacquer, andi-a photographic emulsion on said blushed film.

JOHN SENECA GUMMINGS. 

